I don't follow.
For 20 you would 20x3 = 60 pins
Fo 30 you would need 30x3= 90 pin
How do you figure only 32?
By using multiple chips.
Multiple atmega1284?
I'm not following what you are trying to do.
You haven't written anything about the complete project.
What is the final purpose of reading in 32 RFID-devices that use a Wiegand-interface?
It might well be that achieving the final purpose can be done very differently wih much less problems. As you haven't written anything about this final purpose it is impossible to say.
Hi, it will be used to unlock storage lockers inside a secured building.
So what do you mean by multiple chips??
I think it has already been determined that the MCP23 is not usable.
So it is a security-thing.
Well in my opinion you should use a rather small separate microcontroller for each lockerdoor and use any easier to handle interface as a central unit to which all the 32 microcontrollers are connected to
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